Zeke: Stage One by Ward J. Pyle (Paperback)
$11.99
What comes in is what goes out according to conservation of momentum. However, particles cannot occupy the same space whereas waves superimpose. A medium is needed to explain gravity. How it can exist is according to entropy and covariance of relativity theory. It is explained in this booklet as such, whereas my full book includes history from Aristotle algebra and geometry for verification.